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| United States Patent |
6,096,391
|
|
Muffoletto
, et al.
|
August 1, 2000
|
Method for improving electrical conductivity of metals, metal alloys and
metal oxides
Abstract
A method for improving the electrical conductivity of a substrate of metal,
metal alloy or metal oxide comprising depositing a small or minor amount
of metal or metals from Group VIIIA metals (Fe, Ru, Os, Co, Rh, Ir, Ni,
Pd, Pt) or from Group IA metals (Cu, Ag, Au) on a substrate of metal,
metal alloys and/or metal oxide from Group IVA metals (Ti, Zr, Hf), Group
VA metals (V, Nb, Ta), Group VIA metals (Cr, Mo, W) and Al, Mn, Ni and Cu.
The native oxide layer of the substrate is changed from electrically
insulating to electrically conductive. The step of depositing is carried
out by a low temperature arc vapor deposition process. The deposition may
be performed on either treated or untreated substrate. The substrate with
native oxide layer made electrically conductive is useable in the
manufacture of electrodes for devices such as capacitors and batteries.
| Inventors:
|
Muffoletto; Barry C. (Alden, NY);
Shah; Ashish (East Amherst, NY)
|
| Assignee:
|
Wilson Greatbatch Ltd. (Clarence, NY)
|
| Appl. No.:
|
174132 |
| Filed:
|
October 16, 1998 |
| Current U.S. Class: |
427/580; 427/81; 427/255.4; 427/255.7 |
| Intern'l Class: |
H05H 001/48; B05D 005/12 |
| Field of Search: |
427/580,81,255.4,255.7
|
References Cited
U.S. Patent Documents
| 4351855 | Sep., 1982 | Pinkhasov | 427/37.
|
| 4438153 | Mar., 1984 | Pinkhasov | 427/37.
|
| 4569719 | Feb., 1986 | Coleman | 156/643.
|
| 4609564 | Sep., 1986 | Pinkhasov | 427/37.
|
| 4942844 | Jul., 1990 | Pinkhasov | 118/723.
|
| 4975230 | Dec., 1990 | Pinkhasov | 264/59.
|
| 4978556 | Dec., 1990 | Pinkhasov | 427/37.
|
| 5011638 | Apr., 1991 | Pinkhasov | 264/59.
|
| 5098485 | Mar., 1992 | Evans | 148/272.
|
| 5269898 | Dec., 1993 | Welty | 204/298.
|
Primary Examiner: King; Roy V.
Attorney, Agent or Firm: Hodgson, Russ, Andrews, Woods & Goodyear LLP
Claims
What is claimed is:
1. A method of improving electrical conductivity of metals, metal alloys
and metal oxides comprising:
a) providing a substrate having an electrically insulating native oxide
layer on a surface thereof, said substrate being selected from the group
consisting of Group IVA, Group VA and Group VIA metals, aluminum,
manganese, nickel, copper and stainless steel; and
b) utilizing a low temperature arc vapor deposition process to deposit on
said native oxide layer a metal selected from the group consisting of
Group IA and Group VIIIA metals;
c) whereby said native oxide layer is changed from being electrically
insulating to being more electrically conductive.
2. A method according to claim 1, including sequentially depositing and
intermixing until a predetermined mixing depth is obtained.
3. A method according to claim 1, further including applying a coating on
said native oxide layer whereby said substrate is useable as an electrode
in a capacitor.
4. A method of improving electrical conductivity of metals, metal alloys
and metal oxides comprising:
a) providing a substrate having an electrically insulating native oxide
layer on a surface thereof, said substrate being of a material operative
for use as an electrode in a capacitor; and
b) utilizing a low temperature arc vapor deposition process to deposit on
said substrate surface a metal selected from the group consisting of Group
IA and Group VIIIA metals;
c) whereby said native oxide layer is changed from being electrically
insulating to being more electrically conductive.
5. A method according to claim 4, further including applying a coating of
capacitor electrode material on said native oxide layer.
Description
BACKGROUND OF THE INVENTION
This invention relates to the art of treating metals, metal alloys and
metal oxides, and more particularly to a new and improved method for
enhancing the electrical conductivity of metals, metal alloys and metal
oxides.
One area of use of the present invention is in the manufacturing of
electrodes for capacitors, batteries and the like, although the principles
of the present invention can be variously applied. Metals and metal alloys
have a native oxide present on the surface. This is an insulating layer
and hence if the material is to be used as a substrate for an electrode,
the oxide has to be removed or made electrically conductive.
If the oxide is removed by chemical treatment, such as by etching with an
acid or electrolytic etching to expose the underlying metal, special steps
must be taken in order to complete the electrical contacts before the
native oxide can be regenerated and interfere with the electrical
contacts. Such measures require special apparatus and extremely careful
handling of the materials, all of which adds cost to the fabricating of
electrical devices incorporating these materials to which electrical
contact must be made. Another approach involves removing the oxide layer
and plating the bare substrate metal with an expensive noble metal, such
as silver, gold, or alloys of silver, gold and platinum, or the formation
of an electrically conducting compound on the bare substrate surface. The
materials employed are expensive and the steps required to plate the
substrate are costly and time consuming. In addition, the metal plating or
electrically conducting compound must be disposed on the substrate as a
continuous film for maximum performance. Therefore, the plating or
compound formation typically is carried out after the substrate metal is
formed into its final shape for the electrical device in which it is
incorporated in order to avoid damage to the coating. This, in turn, adds
to the cost and complexity of the manufacturing process.
U.S. Pat. No. 5,098,485 issued Mar. 24, 1992 to David A. Evans proposes a
solution to the oxide problem by altering the native oxide from an
electrically insulating to an electrically conducting condition without
removal of the native oxide layer to expose the underlying metal or alloy.
A solution containing ions of an electrical material is applied to the
native oxide layer, and then the substrate, oxide and applied ions are
heated to an elevated temperature for a time sufficient to incorporate the
ions into the oxide layer to change it from an electrical insulator to an
electrical conductor.
SUMMARY OF THE INVENTION
It would therefore, be highly desirable to provide a new and improved
method for enhancing the electrical conductivity of metals, metal alloys
and metal oxides which does not require additional heat treatment, which
provides control over the density and depth of the material introduced to
the treated surface, which can be performed in a manner preventing
substrate degradation and deformation, and which improves the quality of
the treated surface.
The present invention provides a method for improving the electrical
conductivity of a substrate of metal, metal alloy or metal oxide which
includes depositing a small or minor amount of metal or metals from Group
VIIIA metals (Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt) or from Group IA metals
(Cu, Ag, Au) on a substrate of metal, metal alloys and/or metal oxide from
Group IVA metals (Ti, Zr, Hf), Group VA metals (V, Nb, Ta), Group VIA
metals (Cr, Mo, W) and Al, Mn, Ni and Cu. The native oxide layer is
changed from electrically insulating to electric ally conductive. The
depositing process is a low temperature arc vapor deposition process. This
may be done in a deposition chamber. The deposition may be performed on
either treated or untreated substrate. After deposition the substrate is
available for use as a substrate and no other processing steps may be
necessary.
The method of the present invention advantageously does not require
additional heat treatment and provides control over the density and depth
of the material introduced onto the treated surface thereby not affecting
the bulk of the material. The method can be performed at a temperature
sufficiently low so as to prevent substrate degradation and deformation.
It is believed that the quality of the treated surface is improved by the
method of the present invention. Multiple processing steps may be
incorporated into the method, for example substrate cleaning, oxide
removal and etching. Another advantage is that using a substrate treated
by the method of the present invention will allow the surface thereof to
be treated to passivate it from chemical reaction while still providing
adequate electrical conductivity. Stainless steels having native
insulating oxide layers also can be treated by the method of the present
invention to provide an electrically conductive oxide layer.
A substrate treated by the method of the present invention is ready for
further processing in the manufacture of an electrode for use in
capacitors, batteries and the like. Typically, in the case of a capacitor,
an appropriate electrode material is deposited on the substrate treated
surf ace by techniques well-known to those skilled in the art. Examples of
electrode materials are redox pseudo capacitance materials such as, but
not limited to, oxides and mixed oxides of ruthenium, iridium, manganese,
nickel, cobalt, tungsten, niobium, iron, molybdenum or double layer
materials or under potential deposition materials such as palladium,
platinum, lead dioxide or electro-active conducting polymers such as
polyaniline, polypyrole and polythiophene.
The foregoing and additional advantages and characterizing features of the
present invention will become clearly apparent upon a reading of the
ensuing detailed description together with the included drawing wherein:
BRIEF DESCRIPTION OF THE DRAWING FIGURES
FIG. 1 is a diagrammatic view illustrating the method of the present
invention at one stage thereof;
FIG. 2 is a diagrammatic view illustrating the method of the present
invention at another stage thereof;
FIG. 3 is a diagrammatic view of a substrate after treatment by the method
of the present invention;
FIG. 4 is a diagrammatic view of the substrate of FIG. 3 having electrode
material deposited thereon for use in manufacture of a capacitor
electrode; and
FIGS. 5-7 are graphs depicting impedance spectroscopy scans on substrates
of the type shown in FIG. 4.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
Metals and metal alloys have a native oxide present on the surface which is
electrically insulating and must be removed or made electrically
conductive if the metal or metal alloy is to be used as an electrode in
devices such as capacitors and batteries. Referring to FIG. 1 there is
shown a substrate 10 having an electrically insulating native oxide layer
12 on a surface thereof. In accordance with the present invention, oxide
layer 12 is made more electrically conductive, i.e. changed from
electrically insulating to electrically conductive. Substrates treated by
the method of the present invention include metals and alloys thereof
selected from the group consisting of Group IVA metals (Ti, Zr, Hf), Group
VA metals (V, Nb, Ta), Group VIA metals (Cr, Mo, W), aluminum, manganese,
nickel, copper and stainless steel. They typically have a thickness in the
range from about 0.001 mm. to about 2.0 mm.
In accordance with the present invention, a layer 14 is deposited on the
native oxide layer 12 wherein the layer 14 is a small amount of metal or
metals selected from the group consisting of Group IA metals (Cu, Ag, Au)
and Group VIIIA metals (Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt). The layer 14
is deposited by a low temperature arc vapor deposition process (LTAVD). As
shown in FIG. 2, the process represented diagrammatically by dotted line
20 is carried out by apparatus 22. The deposition may be performed on
either treated or untreated substrate, and the deposition may or may not
be preceded by removal of the oxide from the substrate. This may be done
in the deposition chamber of apparatus 22. The native oxide layer 12 is
changed from electrically resistive to electrically conductive. After
deposition the substrate is available for use as a substrate and no other
processing steps may be necessary.
The depositing of metal 14 on native oxide layer 12 by means of the low
temperature arc vapor deposition process 20 converts the electrically
insulating native oxide layer 12 to a mixed layer 30 on substrate 10 as
shown in FIG. 3 which mixed layer 30 has a degree of electrical
conductivity sufficient to make substrate 10 useable as an electrode in a
device such as a capacitor or battery. In other words, native oxide layer
12 has been converted from being essentially non-conductive, i.e.
insulating, to having an increased and improved degree of electrical
conductivity. Thus, the quality of the treated surface of substrate 10 is
improved in that the surface layer 12 is changed from an insulating,
semiconducting or dielectric state to an electrically conducting state.
The substrate shown in FIG. 3, treated by the method of the present
invention, is ready for further processing in the manufacture of an
electrode for use in capacitors, batteries and the like. Typically, in the
case of a capacitor, an appropriate electrode material 40 as shown in FIG.
4 is deposited on the substrate treated surface by techniques well-known
to those skilled in the art. Examples of electrode material 40 are redox
pseudo capacitance materials such as, but not limited to, oxides and mixed
oxides of ruthenium, iridium, manganese, nickel, cobalt, tungsten,
niobium, iron, molybdenum, or under potential deposition systems such as
palladium, platinum, lead dioxide or electro-active conducting polymers
such as polyaniline, polypyrole, and polythiophene.
The present invention is illustrated further by the following example.
EXAMPLE
A tantalum or titanium substrate similar to substrate 10 shown in FIG. 1 is
first abraded on one side using a 3M Scotch-brite pad of very fine type.
This produces a rough surface on the side to be coated. It is then
degreased and cleaned. This is accomplished by cleaning the foil in an
ultrasonic bath using acetone as a solvent for 10 minutes. Next it is
washed in an ultrasonic methanol bath and then blow dried using dry, clean
compressed air.
The substrate is now ready to be coated with palladium. It is placed in a
Low Temperature Arc Vapor Deposition (LTAVD) apparatus similar to
apparatus 22 of FIG. 2 to be coated. After the sample is loaded into the
apparatus the pressue in the deposition chamber is lowered by a vacuum
pump to 10.sup.-5 -10.sup.-6 Torr. This gets rid of all waste gases,
specially oxygen. In this process oxygen is a contaminant. The pressue is
brought up to the mTorr range by introducing argon into the chamber. The
substrate is biased to 600V and an arc is struck. This arc is now used to
remove the native oxide layer on the tantalum. On completion of the oxide
removal the bias voltage is reduced to 50-100V. The palladium is
evaporated, by the arc, from the electrode and coats the substrate. The
coating thickness is about 0.1 micron. After the deposition is complete
the chamber is back filled with argon and brought back to atmospheric
pressure. The substrate is now ready to be coated with ruthenium oxide, as
the coating provides good electrical contact to the bulk tantalum, for use
in making a capacitor electrode.
FIGS. 5-7 depict impedance spectroscopy scans on substrates treated
according to the present invention and coated with ruthenium oxide for use
as capacitor electrodes. FIG. 5 compares the capacitance of the ruthenium
oxide coating on bare tantalum to capacitance of the ruthenium oxide
coating on tantalum treated according to the present invention. Curve 50
in FIG. 5 is for bare or unprocessed tantalum, and curve 52 is for
tantalum treated according to the present invention by the LTAVD process
20. The relatively lower capacitance of the untreated tantalum is due to
the presence of the insulating native oxide.
FIG. 6 compares the resistance of the ruthenium oxide coating on bare
tantalum to resistance of the ruthenium oxide coating on tantalum treated
according to the present invention. Curve 58 in FIG. 6 is for bare or
untreated tantalum, and curve 60 is for tantalum processed according to
the present invention using the LTAVD process 20. The relatively higher
resistance of the untreated tantalum at the lower end of the frequency
spectrum is due to the presence of the insulating native oxide. FIG. 7
shows the coating behavior with unprocessed tantalum in curve 64, and
tantalum processed according to the present invention in curve 66, using
LTAVD process 20.
Table I presents additional capacitance and resistance data from FIGS. 6
and 7 comparing untreated tantalum with a ruthenium oxide coating to
ruthenium oxide coated tantalum treated according to the present invention
using the LTAVD process 20.
TABLE I
______________________________________
Tantalum Material Cs Rs
______________________________________
Pure Tantalum coated with Ru Oxide
22.30 mF/sq in
521.26 m ohm
Tantalum-LTAVD process coated 473.38 mF/sq in 28.56 m ohm
with Ru Oxide
______________________________________
It is therefore apparent that the present invention accomplishes its
intended objects. While embodiments of the present invention have been
described in detail, that is for the purpose of illustration, not
limitation.
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